The present invention is directed to imager assemblies for miniature camera heads based on solid state sensors e.g., Charged Couple Device (CCD) sensors. These types of cameras are commonly used in imaging systems in minimal access therapy e.g., minimal access surgery, interventional flexible endoscopy, percutaneous interventional radiology, laparoscopy, etc.
Minimal access therapy and/or diagnostics are generally carried out within body cavities and, therefore, the operating field cannot be directly viewed by the person carrying out the operation. For this reason, the ability to carry out such procedures is dependent on the imaging systems that display the images obtained by the camera sensor focused on the scene of the operation.
The imaging systems are usually divided into rigid types of devices (such as laparoscopes) and flexible types of devices (flexible endoscopes). Many of the rigid type devices that are commonly used, known as telescopes, are based on the Hopkins rod-lens system. These devices allow the operator to gain an inner view of the operative field for diagnostics and dissection. The flexible devices that are commonly used are usually based on fiber optic telescopes. These types of flexible endoscopes utilize fiber optics to transmit light into the operative field, and to transfer the image of the operative field to the endoscope eyepiece.
Another type of device that is widely adopted, known as the chip-on-stick technology, is based on optoelectronic instruments. In these devices, an imaging sensor (e.g., CCD) is usually used at the distal end of the telescope or flexible endoscope to record the images produced by an objective lens. Most of the modern miniature cameras that are used in minimal access therapy are of the chip-on-stick variety based on CCD sensors (examples of commercially available devices of this kind are the EndoEYE™ Surgical Videoscopes by Olympus). The optoelectronic systems provide improved image quality and greater light and image sensitivity than the formerly mentioned solutions. However, their performance is affected by the amount of light available in the endoscope, which is dependent upon the size of the illumination means such as the fibers used to transmit the light from a remote source to the operating area, or the Light Emitting Diodes (LEDs) used to illuminate the cavity, e.g., stomach, colon, etc.
The operation of solid state imaging sensors is based on conversion of photons striking the sensor into electron charges (known as the photoelectric effect). The output of the sensor is an electric current, or voltage. The voltage, which is proportional to the number of photons that strike each pixel of the sensor, is amplified by an amplifying device. The amplified signal is usually further processed by converting the voltage signals obtained from the amplifier into equivalent digital signals. Solid-state sensors are utilized to provide images characterized by high-quality and reduced noise levels.
Most chip-on-stick instruments are sensitive to non-chemical sterilization procedures such as autoclaving of the optical components of the imager assembly. This sensitivity results from several causes, one being that the imaging sensor, the objective lens system, and other components of the imager are usually encapsulated utilizing transparent adhesive materials that may lose their transparency as a result of the temperature and pressure involved in the autoclaving process. The loss of transparency is accompanied by a substantial deterioration of the optical qualities of the imager. Another cause of the sensitivity is problems caused by leakage resulting from the pressure of the steam involved in autoclaving.
Additionally, signal distortions result, during medical and industrial procedures, when the environment is hot in comparison to the room temperature or due to residual heat after the autoclaving procedure. It is possible that some of these problems can be overcome by arranging the imager components in a spaced construction utilizing a dedicated enclosure and fastening elements, as described in U.S. Pat. No. 6,019,719. However, although this spaced construction resolves the autoclaving drawbacks discussed above, it also substantially enlarges the imager dimensions. Thus it is not a viable solution when it is necessary to include miniature electrical circuitry in the vicinity of the imaging sensor, as is the case in applications utilizing relatively small imaging sensors.
There is an ongoing effort to reduce the dimensions of the camera heads used in optoelectronic instruments, in order to provide improved penetration and access to bodily organs, e.g., to the lower layer of the lung or deep into the kidney, brain, etc. One of the difficulties that must be solved in designing increasingly smaller camera heads is that the density of photons received by the imaging sensor becomes limited by the sensor's small dimensions. Additionally, the amount of light illuminating the scene is small since the source of illumination (e.g., fiber, LED, or the like) must also be kept very small. Therefore, the signal received from the imaging sensor has to be amplified requiring the use of additional electrical components that are preferably mounted in the vicinity of the imaging sensor. Use of these additional electrical components increases the complexity of the camera heads and multiplies the difficulties in creating miniature and autoclavable imager designs.
An imager assembly is described in U.S. Pat. No. 5,857,963, in which the imaging sensor is mounted on a T-shaped support member 300a, as shown in FIG. 3A. In this assembly the imaging sensor 301 is located in a recess formed on the horizontal member 300b. Circuitry components 313a to 313d, for driving the imaging sensor 301, are mounted on the vertical member 300a. This assembly is beneficial in applications utilizing imaging sensors of relatively large dimensions (e.g., ⅙″ or ¼″ CCDs), wherein all the electrical components 313a to 313d can be compactly arranged on the vertical member 300a without affecting the overall dimensions of the imager assembly.
However, if the imaging sensor used is of relatively small dimensions (e.g., ˜2×2 mm or less), the imager assembly design requires careful consideration of the lengths of the electrical components 313a to 313d. It can be seen that the dimensions of the imager assembly shown in FIG. 3A (in a plane parallel to the plane of the sensor) can be reduced by mounting the imaging sensor on a horizontal member which has same, or smaller, dimensions as those of the imaging sensor 301, as shown in FIG. 3B. Since the lengths of the electrical components 313a to 313d are typically about 1 mm, in applications utilizing imaging sensors approximately equal to, or smaller than, 2×2 mm, the edges of the electrical components will project beyond the virtual edges e1 and e2 defined by the dimensions in the plane of the imaging sensor 301. In this case, the dimensions in the plane parallel to the plane of the sensor of the imager assembly are determined by the thickness of the vertical member 300a and the length of the electrical components 313a to 313d. 
A different imager assembly is described in U.S. Pat. No. 5,754,313. As shown in FIG. 4A, in this assembly two vertical members, 303a and 303b, are used to support a horizontal member 302 on which the imaging sensor 301 is mounted. The electrical components 313a to 313d are mounted on the inner side of the vertical members 303. This assembly suffers from the same drawbacks described hereinabove with regard to FIG. 3A and it is mainly suitable in applications utilizing relatively large imaging sensors.
The assembly shown in FIG. 4B illustrates how these drawbacks could be solved when the imaging sensor 301 utilized is of relatively small dimensions (approximately equal to, or smaller than 2×2 mm). In the assembly shown in FIG. 4B, the electrical components 313a to 313d are arranged in opposite directions on the inner sides of the vertical members 303. But since some of the components cannot be located directly opposite other components, because their combined length exceeds the limited space available, the electrical components must be mounted in a spaced apart arrangement as shown in FIG. 4B. In the arrangement shown in FIG. 4B the width of the imager corresponds to the dimensions of the imager sensor; however to achieve this result the length of the vertical members 303 must be increased over that of the design shown in FIG. 4A in order to provide the required space for all of the electrical components.
In the imager assembly described in U.S. Pat. No. 6,142,930 a different design approach is used. In this assembly the electrical components are mounted on a circuit board positioned behind the imaging sensor. Since this imager is designed to be installed in a shielded pipe, reinforcing plates are required to support the imager, and the imaging sensor leads are bent into an L-shape in order to connect them to the bottom side of the circuit board. This design requires less space than the abovementioned designs, however it is far from optimal as far as miniaturization is concerned and must be improved upon to accommodate the required circuitry and imaging sensors of relatively small dimensions (e.g., to fit into a package having a cross-section of less than or approximately equal to 2×2 mm and having a very short length). The design is not optimal since the CCD is supported by an external housing; the electrical components are placed on a plate within the housing, spaced apart from the CCD; and because of the presence of a separate reinforcement plate for a flexible circuit board.
A similar approach is also used in patent application JP 2001037713A2, wherein two parallel Printed Circuit Boards (PCB's) situated behind the imaging sensor are used for mounting the electrical components. The approach does not make optimal use of the space behind the CCD and therefore the overall dimensions of the imager are not suitable for assemblies using very small imaging sensors (less than or approximately equal to 2×2 mm).
The methods described above do not provide a satisfactory solution to the problem of minimizing the dimensions of imager assemblies that comprise an imaging sensor of relatively small dimensions. The prior art assemblies also fail to provide miniature imager assemblies utilizing very small imaging sensors that maintain their optical qualities even after being repeatedly sterilized utilizing autoclaving procedures.
It is an object of the present invention to provide an imager assembly utilizing an imaging sensor of relatively small dimensions having efficient and minimal packaging confined by the dimensions, of the imaging sensor.
It is another object of the present invention to provide an imager assembly that can be efficiently sterilized utilizing autoclaving sterilization procedures.
It is a further object of the present invention to provide an imager assembly having minimal dimensions and improved flexibility enabling it to be utilized with very small diameter endoscopes.
It is a still further object of the present invention to provide an imager assembly and related electronics comprising means to overcome problems caused by the miniaturization process, e.g., means of reducing the electrical noise, flicker, etc.
It is yet another object of the present invention to provide an imager assembly utilizing an imaging sensor of relatively small dimensions having efficient and minimal packaging and providing high quality and stable images under conditions of relatively low levels of illumination.
Other objects and advantages of the invention will become apparent as the description proceeds.